Sorry about my bad English
I watch anime in 1080P or 720P, but both of them are so slow to load.
The streaming start instantly, almost in no time. but after about 5 seconds, the lag starts.
It can't be any problem with internet speed, I can watch YouTube video in 1080P with no problem.
My system specs:
CPU: Core i7 3610QM Quad Core 2.7Ghz
Memory: 8GB
GPU: GT650M 2GB DDR5
128GB SSD + 500GB HDD

I have a very similar issue. Your internet does not seem the best. That is the only thing holding you down. You could close things in the background, such as Steam, other tabs, and anything that uses the internet. I have noticed closing Steam (which i assume you have, given your computer specs) will allow me to go from SD to 1080p. Slow streams suck, here is something to perhaps improve ur mood:

I have a very similar issue. Your internet does not seem the best. That is the only thing holding you down. You could close things in the background, such as Steam, other tabs, and anything that uses the internet. I have noticed closing Steam (which i assume you have, given your computer specs) will allow me to go from SD to 1080p. Slow streams suck, here is something to perhaps improve ur mood:

After all that amazing grammar, you just had to go and use ur at the very end...